Ikta Solork is a carefree young man who only wants two things in life: a woman on his arm and a place to nap. Unfortunately, his peaceful life is destroyed when war breaks out between the Katjvarna Empire and the neighboring Republic of Kioka. Ikta and his childhood friend, Yatorishino Igsem, join the army as military officers, where they meet the infantryman Matthew Tetojirichi, the sniper Torway Remion, and the medic Haroma Becker on a boat heading for the military exam site. However, after a rogue storm sinks their vessel, the five of them end up in enemy territory near a military outpost. There, they discover that the heir to the Katjvarnan throne, Princess Chamille Kitora Katjvanmaninik, has been taken hostage. The five are able to rescue her, and as a reward, each one of them is granted the title of Imperial Knight—one of the highest honors a soldier can receive. It seems that Ikta will have to put his dream of tranquility on hold, as he must now become the hero he never wanted to be.

After having descended upon this world, the gods have created guilds where adventurers can test their mettle. These guilds, known as "familia," grant adventurers the chance to explore, gather, hunt, or simply enjoy themselves. Dungeon ni Deai wo Motomeru no wa Machigatteiru Darou ka Gaiden: Sword Oratoria begins in Orario, the lively city of adventures. The Sword Princess, Ais Wallenstein, and the novice mage, Lefiya Viridis, are members of the Loki Familia, who are experts at monster hunting. With the rest of their group, they journey to the tower of Babel in hopes of exploring the dungeon underneath. Home to powerful monsters, the dungeon will fulfill Ais's desire to master her sword skills, while bringing Lefiya closer to her dream of succeeding Riveria Ljos Alf, vice-captain of the Loki Familia, as the most powerful mage in the land.

Kouichi Uehara is a fourth grade student living in the suburb of Tokyo. One day, he picks up a large stone which turns out to be a fossil of a baby "Kappa" who has been sleeping underground for the past 300 years, and names it "Coo." They become good friends and Coo starts living with Kouichi's family. However, Coo has a hard time adjusting to life among humans and misses his kind.

The war between the Levamme Empire and the Amatsukami Imperium has been raging for years. In the midst of this struggle, the prince of the Levamme Empire declares his love for Juana del Moral and vows to end the war in one year, as part of his marriage proposal. When the Amatsukami catch wind of this, they assault the del Moral residence, targeting Juana's life. As a last ditch effort to bring the prince his bride, the San Maltilia Airforce hires a mercenary of mixed blood—a bestado—to fly Juana to the Levamme capital in secret. The pilot, Charles, accepts the mission...but traversing an ocean alone, into enemy territory, proves a much more dangerous ordeal than anyone could have anticipated.